Communication in Distributed Systems

Tom Kelliher, CS43

Feb. 22, 1996

Communication Protocols

A set of rules followed by two processes (systems, people) which are communicating. The protocol governs how the communication is carried out.

Examples:

Circuit:

The pathway of communication between two computers. It may be a single wire, or a set of wires connected via switches (routers, gateways, bridges, etc.). The circuit may be dedicated or virtual.

Connection-Oriented protocols (TCP)

Connectionless protocols (IP, UDP)

The OSI Model

(Open Systems Interconnection Reference Model)

Seven layered abstract model of a protocol stack:

Advantages: modularity

Disadvantages: call overhead; size increases due to added headers, trailers

Physical Layer

Ethernet:

ATM:

Data Link Layer

Network Layer

Transport Layer

Session Layer

Presentation Layer

``Library''-type functionality

Application Layer

User- System-Level utilities:

Introduction to TCP/IP

Some of the protocols:

Message transmission example:

``Gluing'' Networks Together

IP Addresses

Form:

Encapsulation

  1. Data
  2. Application layer
  3. TCP/UDP layer --- TCP frame
  4. IP layer --- IP datagram
  5. Ethernet layer --- ethernet frame: 46--1500 bytes (MTU)

Demultiplexing

Process Communication

How do processes on separate machines communicate?



Thomas P. Kelliher
Wed Feb 21 17:07:49 EST 1996
Tom Kelliher